Switched reluctance motor

ABSTRACT

In a switched reluctance motor and control system for such a motor, a rotor comprises four salient poles each having a width of about 50-degrees, and a stator has six salient poles each having a width of about 30-degrees. One Excitation winding is mounted around each stator salient pole and these are connected in series. An excitation drive circuit supplies a dc excitation current to each excitation winding to excite the motor in accordance with an excitation command signal. A torque-current drive circuit renders a current, whose magnitude in accordance with a torque command, to flow into torque windings mounted one round on each of the six stator salient poles successively according to the angle of rotation of the rotor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a switched reluctance motor, and moreparticularly to a low cost switched reluctance motor which can be usedas a general-purpose industrial motor. The invention relates also tosuch a motor which is useful as a high-speed motor in which acentrifugal force is a problem in view of a rotor's strength rather thana rotor is solid.

2. Description of the Related Art

In order to rotate the high-speed-rotation shaft of a machine tool in,for example, a machining center, a motor requires approximately 100 mmdiameter rotor and at least 30,000 rpm.

In the described use, it has currently been common to employ aninduction motor. In order to resist to the centrifugal force, the rotorslot is often kept closed and also the coil ends of the rotor are oftenreinforced.

However, these conventional systems are expensive and inevitably adoptthe second best reinforced structure with some sacrifice of the motorcharacteristics.

Attempts have been made to improve the structures of such conventionalreinforced motors. To this end, studies on switched reluctance motorsrelating to their possibilities for increased rotor strength are commonwith some of the resulting ideas being put into practice.

A typical example of these conventional switched reluctance motors isshown in FIG. 23 of the accompanying drawings. A drive algorithm for themotor is shown in FIG. 24. A rotor 2 is in the form of a simple laminatebody composed of a plurality of axially arranged silicon steel disks.Because of the increased strength of the rotor 2, this conventionalmotor meets one handle for high-speed rotation.

A stator 1 of the motor of FIG. 23 has six salient poles 20 each havinga width of approximately 30 degrees in terms of angle of rotation of therotor. Six windings are mounted one round each stator salient pole 20.The rotor 2 has four salient poles 21 each having a width ofapproximately 30 degrees in terms of rotor's rotational angle.

In operation, for generating a counterclockwise rotational torque inFIG. 23, currents are supplied to flow in the windings indicated by TC1,TC2 and TF1, TF2 to attract the rotor salient poles. At that point, thecurrents to flow in the windings TC1, TC2 and those to flow in thewindings TF1, TF2 are opposite in direction in such a manner thatprospective magnetic fluxes pass through the rotor 2. Further, when therotor salient poles have reached the stator salient poles associatedwith the windings TC1, TC2 as the rotor 2 is rotated counterclockwise,generation of the rotational torque will then terminate. At that point,those counterclockwise next to these rotor salient poles approach thestator salient poles associated with the windings indicated by TE1 TE2;if no current is supplied to flow in the windings TC1, TC2 and thecurrents are supplied to flow in the windings indicated by TE1, TE2 andTB1, TB2, then a counterclockwise rotational torque will be generated.Thus if suitable successive currents are supplied to flow in theindividual stator windings one after another, successive rotationaltorques will be generated.

Likewise, for generating a clockwise rotational torque in FIG. 23,currents are supplied to flow in the windings indicated by TB1, TB2 toattract the rotor salient poles.

Variation of the torque to be generated depends on the current of eachwinding and the relative position of the stator and rotor, but does notin principle depend on the speed of rotation of the rotor.

A practical example of a power amplifier section of the drive system forthe switched reluctance motor of FIG. 23 will be described withreference to FIG. 5 which shows the common circuit to be used in thepresent invention. A winding E corresponds to the windings TA1, TA2 ofFIG. 23 and a winding WD corresponds to the windings TD1, TD2 of FIG.23; these two windings WA, WD are opposite to each other in turning. Thecurrent IAD to flow in the winding WA, WD is controlled accurately withrespect to the current command value by PWM control using the differencebetween a current command and the detected value of the current IAD likethe very ordinary, non-illustratedmotor-current control. In amicroscopic operation, a voltage is applied to the windings WA, WD byrendering transistors 8, 9 to assume the ON state, so the current IADwill be increased. If the transistors 8, 9 are rendered to assume theOFF state, magnetic energy and dynamic energy caused by the flowingcurrent at that time are supplied back to DC power sources VS, VL viadiodes 10, 11 to gradually reduce the current. As the foregoingoperation is repeated, the average current of the currents IAD withrespect to the current command value can be controlled. The currentcontrol for the remaining two phases is controlled in the same manner.

Of symbols used in FIGS. 5 and 23 to designate the windings andcurrents, alphabetical characters A, B, C, D, E, F indicate theindividual stator magnetic poles of the motor.

The drive algorithm for the switched reluctance motor of FIG. 23 isshown in FIG. 24. The horizontal axis RA is the angular position of therotor in FIG. 23. For generating a counterclockwise torque, the currentshaving the characteristics of FIGS. 24(a), 24(b), and 24(c) are suppliedto flow in the associated windings. For generating a clockwise torque,the currents having characteristics of FIGS. 24(d), 24(e), and 24(f) aresupplied to flow in the associated windings. In either case a largercurrent amplitude will result in a larger torque.

Advantages of conventional switched reluctance motors include: (1) themanufacturing cost is low because the motor structure is simple and,particularly, the structure of the stator windings is simple; (2) theentire length of the motor is relatively short because the coil ends ofthe stator windings can be shortened; (3) high-speed rotation can berealized in a physical manner because the rotor has sufficient strength;and (4) the drive circuit can be simplified because the drive algorithmis simple so that only one-way flow of the current is needed.

However, certain disadvantages accompany such conventional motors. Forexample, a control algorithm is needed to smooth the relationshipbetween the electric energy supplied and the magnetic energy accumulatedinside the motor and the mechanical output energy to eliminate largetorque ripples. In an effort to solve this problem, a current controlmethod has been proposed in which the current is compensated so as tocompensate torque ripples and the compensated current is then suppliedto flow in the associated winding. However, this proposed currentcontrol method creates additional problems. Further, the intermittenttorque generated by the individual stator salient pole would, along withthe torque ripples, contribute to stator deformation, thus increasingvibration and noise while the motor is driven. As can be seen from thecharacteristics of FIGS. 24(a) through 24(f), it is in fact possible fora torque opposite to that desired to be generated.

For high-speed rotation, a very-high-speed current switch is essential.Also, as supply and regeneration of the magnetic energy inside the motormust be carried out frequently, only a limited power factor can beachieved.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved switched reluctance motor and an improved control system whichsolves the above described problems.

As a general advantageous feature, the improved motor experiences lesstorque ripple from a basic algorithm view point because torques to begenerated on the individual rotor salient poles can be continuous forthe rotor axis.

In a specific motor structure of the present invention, as shown in FIG.1, excitation windings independent of torque windings are mounted oneround for each stator salient pole and excitation currents are suppliedto flow in the corresponding excitation windings of all of the statorsalient poles as shown in FIG. 4.

Alternatively, the excitation windings may be omitted from theindividual stator salient poles, and instead, one permanent magnet maybe arranged at each stator salient poles as shown in FIG. 9.

As shown in FIGS. 1 and 2, the width of the stator salient poles isapproximately 30 degrees, and the number of stator salient poles is 6.And the width of rotor salient poles is 40 degrees with a 5-degreestructural skew, and the number of the rotor salient poles is 4.

The reluctance motor may be equipped with a torque-current controlsection for controlling a torque current to flowing in each torquewinding of the stator.

The excitation windings may be omitted, and the torque winding may havea torque-current control section for superposing the excitation currentover the torque winding.

Two sets of windings are mounted round each stator salient pole, andtransistors are rendered to assume the ON state to supply voltage andcurrent to one set of stator windings to increase the current. Todecrease the current, the transistor is rendered to assume the OFF stateto supply energy back to the power sources via a diode by the voltageinduced by the other set of stator windings, which areelectromagnetically coupled, thus decreasing the total stator current ofthat stator.

As a measure to minimize torque ripples, the rotor or stator is axiallydivided into several parts, which are shifted in the direction ofrotation by 1/2 of cycle of the frequency component of the torqueripples to be generated by the motor.

For high-speed rotation, intermediate taps of the windings mounted roundthe stator salient poles lead to outside or two or more sets of windingsare mounted on each stator salient pole, and the motor is equipped witha switching circuit for switching over between a first state in whichthese windings are connected in series and a second state in which onewinding is connected to part of another winding.

In another specific motor structure, as shown in FIG. 17, the statorcomprises six stator magnetic poles having a width smaller than, butsubstantially equal to, 60 degrees in angle of rotation of the rotor.Excitation windings are mounted one round each stator magnetic pole. Theexcitation windings are connected in series in such a manner that eachadjacent pair of excitation windings are opposite in turning (aninverted-series-connection). Torque windings mounted round the statormagnetic poles are of a three-phase type and are angularly spaced apartone another by 180 degrees. These torque windings are aninverted-series-connected pair diametrically opposed with respect to thecenter of rotation of the rotor. The rotor has two rotor salient poleshaving a width ranging from 60 to 120 degrees in angle of rotation ofthe rotor.

One example control system for the motor is equipped with atorque-current drive circuit for causing, when a torque command ispositive, a current having a magnitude in accordance with the torquecommand to flow in the torque winding of the stator magnetic pole atwhich a counterclockwise end of the associated rotor salient poles andfor causing, when the torque command is negative, the current to flow inthe torque windings of the stator magnetic pole at which a clockwise endof the associated rotor salient poles.

A control algorithm for varying a torque current is also proposed.

In another specific switched reluctance motor, common windings aremounted one round each stator salient pole, serving as both excitationand torque windings.

Another example of control system for the motor has acommon-winding-current drive circuit for obtaining an excitation currentsuch as to excite the motor in accordance with an excitation commandsignal, for obtaining a torque current such as to have a magnitude inaccordance with a torque command, which represents a counter clockwisetorque when it is positive, and to flow in the common winding of eachstator salient pole, at which a counterclockwise end of the associatedsalient pole is located when the torque command is positive or aclockwise end of the associated salient pole is located when the torquecommand is negative, and for rendering a composite current, which is asum of the excitation current and the torque current, to flow in eachcommon winding.

In a specific structure of the motor, as shown in FIG. 1, excitationwindings are mounted one round each of stator salient poles and areconnected in series, and excitation currents are supplied to flow in thecorresponding excitation windings of all of the stator salient poles asshown in FIG. 4.

Alternatively, the excitation windings may be omitted from theindividual stator salient poles, and permanent magnets may instead bearranged one at each of the stator salient poles as shown in FIG. 9 toexcite the motor.

As shown in FIGS. 1 and 2, the width of the stator salient poles isapproximately 30 degrees, and the number of stator salient poles is 6.And the width of rotor salient poles is 40 degrees with a 5-degreestructural skew, and the number of the rotor salient poles is 4.

A control system for causing a torque current to flow in each statortorque winding in the switched reluctance motor controls the amplitudeof the torque current in accordance with the angle of rotation of therotor. This current amplitude control, namely, varying of the current isperformed by a current control section for varying the current of thetorque winding of each stator salient pole while the associated rotorsalient pole is located perfectly in or out of confronting relationshipwith the stator salient pole through its circumferential surface. Morespecifically, the current control section is operable for controlling,during strenuous operation, a torque current in the torque windings oneach stator salient pole in such a manner that a current value of thetorque current is increased from zero to a current value IP1corresponding to a torque command value TCM while each stator salientpole is located within the width of the associated rotor recess, thatthe torque current flows in the corresponding torque winding to generatea rotational torque while each rotor salient pole reaches each statorsalient pole surrounded by the corresponding torque winding and that thetorque current is decreased from the current value IP1 to zero whileeach stator salient pole is located within the width of the associatedrotor salient pole, and also for controlling, during regenerativeoperation, the torque current in the stator winding on each statorsalient pole in such a manner that the torque current flows in thestator windings as its current value is increased from zero to an torquecurrent value IP1 corresponding to an torque command value TCM whileeach rotor salient pole is located within the width of the associatedrotor salient pole, that a regenerative rotational torque is generatedwhile each rotor salient pole is moved away from the associated statorsalient pole surrounded by the torque winding and that the torquecurrent in the stator windings on each stator salient pole is decreasedfrom the torque current value IP1 to zero while each stator salient poleis located within the width of the associated stator recess as eachstator salient pole is moved away from the associated stator statorpole.

Alternatively, the excitation windings may be omitted, and excitationcurrent may be superposed in the torque windings. The merit of thisalternative is that the motor winding structure is simplified in theabsence of excitation windings and that the drive circuit structuresimplified in the absence of excitation windings. On the other hand, theload of the excitation current component is born on the torque-currentdrive circuit, which is large in circuit scale.

In the excitation-winding-free motor structure, the excitation currentcomponent for generating a torque opposite to the torque command may beeliminated.

Two sets of windings are mounted around each stator salient pole, andtransistors are rendered to assume the ON state to supply voltage andcurrent to one set of stator windings to increase the current. Todecrease the current, the transistor is rendered to assume the OFF stateto supply energy back to the power sources via a diode by the voltageinduced by the other set of stator windings, which areelectromagnetically coupled, thus decreasing the total stator current ofthat stator.

As a measure to minimize torque ripples, the rotor or stator may beaxially divided into halves, which are shifted in the direction ofrotation by 1/2 of cycle of the frequency component of the torqueripples to be generated by the motor. Further, the similarly dividedrotor or stator is overlapped over this divided rotor or stator to forma double-pair laminate, in which the succeeding pair is shifted in thedirection of rotation by 1/2 of cycle of the frequency component withrespect to the preceding pair. The result is that the two frequencycomponents of the torque ripples can be further minimized.

For high-speed rotation, intermediate taps of the windings mounted roundthe stator salient poles lead to outside, or two or more sets ofwindings are mounted on each stator salient pole, and the motor isequipped with a switching circuit for switching over between a firststate in which these windings are connected in series and a second statein which one winding is connected to part of another winding. Thus, bycontrolling the low-voltage windings, it is possible to control thehigh-speed rotation.

Although the polarity of each rotor salient pole depends on the angularposition of the rotor, the two-pole rotor provides a constant magneticflux all times. It is therefore possible to make the magnetic energyinside the motor basically constant irrespective of the position ofrotation of the rotor. When the excitation current is supplied to flowin all of series-connected excitation windings, any of the excitationwindings is decreased in magnetic flux with the rotation of the rotor togenerate a negative voltage and, at the same time, any of the remainingexcitation windings is increased in magnetic flux to generate a positivevoltage. Accordingly, the total voltage of the series-connectedexcitation windings is only the voltage effect of the winding resistanceso that basically a voltage causing the magnetic flux to vary will begenerated. Consequently, a very simple excitation control of the drivesystem will suffice. Regarding the gap between adjacent stator magneticpoles, if it is small, its bad influence of the gap-will be small, andeven if it is large, it is possible to minimize the bad influence byskewing the rotor or stator.

Because torque generation is achieved by magnetic attraction, it ispossible to generate a desired torque inside the stator magnetic poleconfronting the rotor salient pole by supplying a torque current to flowin the torque winding of the stator magnetic pole. By repeating thisoperation successively with respect to the torque windings of theremaining stator magnetic poles, successive rotational torques can beobtained.

The stator magnetic pole is located perfectly in or out of confrontingrelationship with the entire circumferential surfaces of the associatedrotor salient pole, namely, no induction voltage of each windings isgenerated. By varying the current of the torque windings using thisrange of rotational angle, it is possible to perform current controlwith less torque ripples.

Further, as a measure to reduce the total cost of the switchedreluctance motor and the drive system, a plurality of regenerativewindings are mounted one on each stator magnetic pole. For utilizingpart of the magnetic energy of each stator magnetic pole to rotate therotor and supplying part of the remaining magnetic energy to flow backto the power source, a motor-energy regenerating circuit is composed ofa plurality of diodes each connected in series between each of theregenerative windings and the power source of the motor. Each diode hasan anode connected to a low-voltage side of the power source and acathode connected to a high-voltage side of the power source. Thismotor-energy regenerative circuit is simple in structure as the numberof either the power transistors or the diodes can be reduced to 3, ascompared with 6 in a conventional regenerative circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example typical switchedreluctance motor of the present invention;

FIG. 2 is a diagram showing surfaces of salient poles of a rotor of theswitched reluctance motor as unfolded in plan in the direction ofrotation of the rotor;

FIG. 3 is a block diagram showing a preferred embodiment of a motorcontrol system of the present invention;

FIG. 4 is a diagram showing an example of field-current control sectionFD;

FIG. 5 is a circuit diagram showing a power amplifier circuit PW of acurrent control section;

FIG. 6 is a graph showing the magnetic characteristics of magneticmaterial of the motor;

FIGS. 7(a) through 7(f) are control characteristic charts of a controlsystem of the present invention;

FIGS. 8(a) through 8(f) are control characteristic charts of the controlsystem of the present invention;

FIG. 9 is a cross-sectional view of a switched reluctance motor of thepresent invention;

FIG. 10 is a cross-sectional view of another switched reluctance motorof the present invention;

FIGS. 11(a) through 11(f) are control characteristic charts of a controlsystem of the present invention;

FIGS. 12(a) through 12(f) are control characteristic charts of thecontrol system of the present invention;

FIG. 13 is a cross-sectional view of still another switched reluctancemotor of the present invention;

FIG. 14 is a circuit diagram showing windings of and a power amplifiercircuit PW of the switched reluctance motor;

FIGS. 15(a) through 15(g) are control characteristic charts of a controlsystem of the present invention;

FIG. 16 is a diagram showing the construction of the windings of theswitched reluctance motor;

FIG. 17 is a cross-sectional view showing a motor according to anotherembodiment of the present invention, which is controlled by the controlsystem of the present invention;

FIGS. 18(a) through 18(e) are control characteristic charts of thecontrol system of the present invention;

FIGS. 19(a) through 19(e) are control characteristic charts of thecontrol system of the present invention;

FIG. 20 is a cross-sectional view showing another motor, which isaccording to still another embodiment, to be controlled by the controlsystem of the present invention;

FIG. 21 is a block diagram showing a motor control system according toanother embodiment of the present invention;

FIGS. 22(a) through 22(d) are control characteristic charts of thecontrol system of the present invention;

FIG. 23 is a cross-sectional view of a conventional switched reluctancemotor; and

FIGS. 24(a) through 24(f) are control characteristic charts of aconventional switched reluctance motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention are particularly useful whenapplied to a switched reluctance motor and related control system,preferred embodiments of which will now be described in detail withreference to the accompanying drawings.

FIG. 1 shows a switched reluctance motor according to a first embodimentof the present invention.

Reference number 1 in FIG. 1 is a stator surrounding a rotor andequipped with six stator salient poles 20 each having a width ofsubstantially equal to 30 degrees in angle of rotation of a rotor.Excitation windings and torque windings are mounted round each statorsalient pole 20. In the excitation windings, those indicated by HA3, HA4are WAF windings, those indicated by HB3, HB4 are WBF windings, thoseindicated by HC3, HC4 are WCF, those indicated by HD3, HD4 are WDFwindings, those indicated by HE3, HE4 are WEF, and those indicated byHF3, HF4 are WFF windings. In the torque windings, those indicated byHA1, HA2 are WAT windings, those indicated by HB1, HB2 are WBT windings,those indicated by HC1, HC2 are WCT windings, those indicated by HD1,HD2 are WDT windings, those indicated by HE1, HE2 are WET windings, andthose indicated by HF1, hF2 are WFT windings. A, B, C, D, E, F of WAF,WBF, WCF, WDF, WEF, WFF, WAT, WBT, WCT, WDT, WET, WFT designate theindividual stator salient poles.

Each of the stator 1 and the rotor is composed of silicon steel diskslaminated along its axis.

The rotor is equipped with four salient poles 21 arranged around a rotorshaft 2 and each having a width of approximately 40 degrees in angle ofrotation of the rotor and individually skewed by 5 degrees duringlamination.

FIG. 2 is a diagram showing circumferential surfaces of the four salientpoles of the rotor as unfolded in plan in the direction of rotation ofthe rotor. Accordingly the width of each rotor salient pole isapproximately 50 degrees including skewed portions, as shown in FIG. 2.

FIG. 3 shows a speed control system for the motor. NRM designates themotor of FIG. 1.

E designates an encoder for detecting an angle of rotation of the rotorto output a position detection signal PS.

PSC designates a velocity detecting section for detecting a velocitysignal VEL based on the input of the position detection signal PS.

VC designates a velocity control section composed of a velocitycontroller VCC for obtaining a torque command signal TCM based on theinput of a velocity command VCM and the velocity signal VEL and a fieldcurrent controller FCC for obtaining and outputting a field currentcommand FCM based on the input of the velocity command VCM and thevelocity signal VEL.

FD designates a field-current control section for causing a fieldcurrent ID to the motor NRM in accordance with the field current commandFCM. The field current command FCM is a constant value when the motorNRM is rotating at an rpm less than a predetermined base value and avalue gradually descending with the rpm of the motor when the last-namedrpm. is larger than the base value. This is because a motor inductionvoltage will fall below a power source voltage when the rpm. is largerthan the base value. The typical so-called field attenuation controlmethod for reducing the field current command FCM with rpm. is a methodin which the field current command FCM plays as a reciprocal function ofthe rpm. of the motor when the rpm is over the base value. If it issmall, the torque command is practically effective as a small fieldcurrent command value in not only reducing possible heat the motor mightgenerate but also minimizing a possible torque ripple.

FIG. 4 is a diagram showing the manner in which a power circuit isconnected to the individual excitation windings in the field currentcontrol section FD. Each excitation winding WAF, WBF, WCF, WDF, WEF, WFFmounted around each stator salient pole is reversely wound with respectto those round adjacent stator salient poles so that each adjacent pairof stator salient poles will be respectively polarized as N and S polesas shown in FIG. 1 when direct current flows in these excitationwindings as shown in FIG. 4. The label 5 designates a field currentcontrol circuit for appropriately controlling a field current ID; 6, adrive transistor; 4, a flywheel diode.

As shown in FIG. 1, the area of portions at which the rotor salientpoles confront the stator salient poles remains constant, irrespectiveof the position of rotation of the rotor, and every stator salient poleis polarized as an N or S pole so that, although the polarity ofmagnetic flux will change over between N and S poles depending on theangular position of the rotor, the absolute value of the magnetic fluxwill be constant all times. When an excitation current flows in theindividual excitation windings all connected in series, the totalmagnetic flux of the motor does not vary even when the rotor rotates,and therefore any excitation winding will decrease in magnetic flux togenerate a negative voltage and, at the same time, any other excitationwill increase in magnetic flux to generate a positive voltage, thusresulting in that a total voltage of the series-connected excitationwindings will give a voltage effect of the resistance component of thewindings but will basically not generate any voltage due to thevariation of magnetic flux. Therefore, a very simple excitation controlby the field current control section as shown in FIG. 4 will besufficient. Further, if such a resistance of the excitation windings asto satisfy (voltage VS-VL)=(excitation current ID)×(total resistance ofexcitation windings) is selected, only connecting the excitationwindings to the power source is needed, so the excitation circuit FD ofFIG. 4 is also not needed.

The same result as described above can be achieved when each three phaseexcitation windings is divided two sets and connected to an excitationcurrent drive circuit respectively. The excitation circuit FD is notlimited to the configuration shown FIG. 4.

The functional advantage of the motor of FIG. 1 is that since magneticenergy is automatically be exchanged between the excitation windings,the load of the torque current control system will be reduced, ascompared to the conventional concept in which the voltage load of theexcitation current drive of the conventional control system will rise,particularly during high-rpm control.

The phenomenon that no rotational torque is generated as magnetic energyinsures that positive and negative torques generated at opposite ends ofthe rotor cancel each other. Therefore, no reluctance torque will not begenerated in the motor as a whole, while only excitation current flowsin the excitation windings. When the stator salient pole and the rotorsalient pole are moved toward or away from each other, a slightdiscontinuity will occur in their boundary region, but basically atorque ripple will be small. Possible negative influence of this torqueripple can be minimized by tilting or skewing rotor or stator.

As will be described below, a rotational torque can be generated byadding a torque current while this excitation current flows in theexcitation windings. At that time the power factor of the torque currentis large as the current and the voltage substantially coincide in timephase.

TC designates a torque control section responsive to the input of thetorque command signal TCM and the position detection signal PS foroutputting individual phase current commands IADS, IBES, ICFS of themotor NPM and voltage feedforward signals VAD, VBE, VCF of theindividual phases as an end voltage of each phase is assumed.

TD designates a current control section that obtains, for one phase, thedifference between detected values of the current command IADS and thecurrent IAD to perform a process, such as a proportional integralcontrol by a current controller ICR, then adds the voltage feedforwardsignal VAD and outputs the voltage command signal to the power amplifiercircuit PW. The procedure is followed for the remaining phases.

The power amplifier circuit PW, for the phase of the current IAD, isresponsive to the input of the voltage command signal to drivebelow-described transistors 8, 9 of FIG. 5 by the very ordinary PWMoperation and supplies a current IAD to the motor NRM.

FIG. 5 shows the manner in which power circuits of the power amplifiercircuit PW are connected with the individual torque windings of thestator. WAT designates torque windings indicated by HA1, HA2, and WDTdesignates torque windings indicated by Hd1, HD2. 8, 9 designate drivetransistors, and 10, 11 designate regenerative flywheel diodes. Thetoque windings WAT and WDT are mutually reversely wound and areconnected in series. The current direction of the excitation windingsand the current direction of the torque windings in each stator salientpole coincide. When the torque current IAD flows, the transistors 8, 9will be switched on; when the transistors 8, 9 are switched off, thecurrent IAD will be supplied back to the power sources VS, VL via theflywheel diodes 10, 11. VL is a common line of the power circuits.

As the result of this PWM control, the current IAD will become pulsatilewith respect to the current command IADS as processed by the PWMcontrol, but the general current will be controlled in accordance withthe command. Accordingly, the average current value will be inaccordance with the current command IADS.

Regarding current control for the current IBE of the windings WBT, WETand the current ICF of the windings WCT, WFT, the power amplifiercircuit PW performs the same process as for the current LAD.

The relation between the excitation current and torque current and themagnetic energy inside the motor will now be described quantitatively.FIG. 6 is a graph showing a magnetic characteristic of the motor as amodel; the horizontal coordinate is the electromotive force H and thevertical coordinate is the magnetic flux density B. When the excitationcurrent flows in the excitation windings in such a manner that theelectromotive force will be H0, the magnetic flux density of the excitedmagnetic circuit of the motor will be B0 with an operating point beingX0. The magnetic energy inside the magnetic circuit is indicated by atriangle OX0B0. When the torque current flows in the torque windings bythe difference between H1 and H0, the operating point shifts to X1 sothat variation of the magnetic energy inside the motor will be small,e.g. zero in FIG. 6. Thus, since the variation of magnetic flux due tothe torque current in the torque-current variation control is small,inductance is small and controllability is high.

The relation between the torque generation and the current in theindividual torque winding is shown in FIGS. 7(a) through 7(f) and 8(a)through 8(f) as characteristics relation between the individual currentvalue and the rotational angle RA.

In FIG. 1, RA is an angle between the horizontal center line of therotor and the end of counterclockwise rotation of the rotor salientpole.

The relation between the torque generation and the current in theindividual torque winding is shown in FIGS. 7(a) through 7(f) and 8(a)through 8(f) as characteristics relation between the individual currentvalue and the rotational angle RA.

First, the value of the excitation current ID is constant ID1irrespective of the rotational angle RA.

Assuming that the rotational angle RA gradually increases from zero, inother words, the rotor is rotating counterclockwise, a constant torquewill be generated as the individual currents flow in the correspondingwindings with a phase difference of 60 degrees in the rotor's rotationalangle RA as shown in FIGS. 7(a), 7(b) and 7(c). A range of the rotor'srotational angle RA from 30 to 150 degrees is shown on an enlarged scalein FIGS. 7(d), 7(e) and 7(f), with reference to which the detaileddescription will now be made. Solid lines represent the flowing current,and dash-and-dot lines represent the induction voltage induced by thetorque winding.

The description will begin with the induction voltage induced by thewinding of each phase.

When the rotor is rotating at a constant rpm. in the counterclockwisedirection CCW, the voltage to be induced by the torque windings WAT, WDTis proportional to the ration of variation of magnetic flux crossingeach winding. Therefore, as shown in FIG. 7(d), while RA is within arange of 30 to 35 degrees, a negative voltage will begin to be generatedas a skewed part of end of the rotor begins to be displaced off theposition of the confronting stator salient pole. And within a range of35 to 60 degrees, a constant voltage -V1 will be induced as the rotorsalient pole begins to be displaced off the position of the confrontingstator salient pole with rotation, and within a range of 60 to 65degrees, the voltage will be gradually reduced to zero as the end of theskewed portion of the rotor salient pole is displaced off theconfronting stator salient pole. Within a range of 65 to 75 degrees, novoltage will be generated as the rotor salient pole does not confrontthe stator salient pole; within a range of 75 to 80 degrees, a positivevoltage will begin to be increased as the skewed part of end of therotor begins to be located within the width of the confronting statorsalient pole; and within a range of 80 to 105 degrees, a constantvoltage V1 will be induced as the rotor salient pole confronts thestator salient pole by an increasing overlapping width with rotation.Within a range of 105 to 110 degrees, the voltage will be graduallylowered to zero as the counterclockwise (CCW) end of the skewed part ofthe rotor begins to be displaced off the stator salient pole; and withina range of 110 to 120 degrees, no voltage will be generated as thestator salient pole is located within the width of the rotor salientpole. The cycle of process will then be repeated.

The current to flow in the torque windings WAT, WDT will next bedescribed. As a practical method dealing with current flow, the currentis controlled to vary within the time range when no voltage isgenerated, causing no torque to occur. Since the form of A3 variation ofthe current will influence on the motor torque within that time period,it is possible to vary the current sharply and easily when the maximumvoltage is applied. The current is increased from zero to IP1 while therotor's rotational angle RA is within a range of 60 to 75 degrees, thenis kept constant at IP1 while RA is within a range of 75 to 110 degrees,and is then lowered from IP1 to zero while RA is within a range of 110to 120 degrees. Because the power is a product of the current and thevoltage, a torque proportional to the voltage within the RA range from75 to 110 degrees will be generated as energy is supplied to the motor.

The voltage and current of the remaining torque windings WBT, WET are asshown in FIG. 7(e). Their phases are delayed by 60 degrees from those ofFIG. 7(d). Likewise the voltage and current of the torque windings WCT,WFT are as shown in FIG. 7(f), and their phases are delayed by 120degrees from those of FIG. 7(d). The total torque of three phases ofFIGS. 7(a), 7(b) and 7(c) takes a constant value irrespective of therotational angle of the rotor.

The manner in which a clockwise torque corresponding to the currentamplitude IP1 is continuously generated as the rotor is rotating in thecounterclockwise direction CCW will now be described. This is the casethe motor performs a regenerative operation.

First, the value of the excitation current ID is constant ID1irrespective of the rotational angle RA.

Assuming that the rotational angle RA gradually increases from zero,namely, the rotor is rotating counterclockwise, a constant torque willbe generated as the individual currents flow in the correspondingwindings with a phase difference of 60 degrees in the rotor's rotationalangle RA as shown in FIGS. 8(a), 8(b) and 8(c). A range of the rotor'srotational angle RA from 30 to 150 degrees is shown on an enlarged scalein FIGS. 8(d), 8(e) and 8(f), with reference to which the detaileddescription will now be made. Solid lines represent the flowing current,while broken lines represent the induction voltage induced by the torquewinding.

The induction voltages induced by the windings of the individual phasesare the same as those of FIGS. 7(d), 7(e) and 7(f) in terms of therotational direction and excitation current.

The current to flow in the torque windings WAT, WDT will next bedescribed. As a practical method dealing with current flow, the currentis controlled to vary within the time range when no voltage isgenerated, causing no torque to occur. The direction of the torque isopposite and hence the timing at which the current flows is opposite, ascompared to the case of FIGS. 7(a) through (f).

In FIG. 8(d), the excitation current is maintained at a constant valueIP1 while the rotor's rotational angle RA is within a range of 30 to 65degrees, then is decreased from PI1 to zero within a range of 65 to 75degrees, is kept zero within a range of 75 to 110 degrees and isincreased from zero to IP1 in a range of 110 to 120 degrees. Because thepower is a product of the current and the voltage, the power is negativewithin a range of 75 to 110 degrees so that energy will be supplied backto the power source and a braking torque will be generated within thatrange. The magnitude of this braking torque is proportional to thevoltage.

The voltage and current of the remaining torque windings WBT, WET are asshown in FIG. 8(e), and their phases are delayed by 60 degrees fromthose of FIG. 8 (d). Likewise, the voltage and current of the torquewindings WCT, WFT are as shown in FIG. 8(f), and their phases aredelayed by 120 degrees from those of FIG. 8(d). The total torque ofthree phases of FIGS. 8(a), 8(b) and 8(c) takes a negative constantvalue irrespective of the rotational angle of the rotor. Accordingly, aconstant braking torque is generated.

Of the induction voltages indicated by dash-and-dot lines in FIGS. 7(d)to 7(f) and 8(d) to 8(f), the induction voltage while the current ineach phase flows may be treated as the voltage feedforward signal VAD,VBE, VCF.

The generation of torque is associated with the current in each phaseand with the rotational position, but is not associated with therotational direction and the rotational speed.

FIG. 9 shows another switched reluctance motor according to a secondembodiment of the present invention.

The motor of FIG. 9 differs from that shown in FIG. 1 in that theexcitation windings are omitted and, instead, permanent magnets 22 areinserted one in each stator salient pole for generating electromotiveforces. The drive system and control method for this motor aresubstantially similar to those for the motor of FIG. 1. In the absenceof the excitation windings, an improved motor efficiency can beachieved. Further, the motor of this embodiment is suitable for use as aservo motor, which must be stopped by a dynamic brake in case of powerfailure or emergency. In the permanent-magnet-free motor of FIG. 1, itis difficult to make a dynamic brake.

FIG. 10 shows still another switched reluctance motor according to athird embodiment of the present invention.

In the motor of FIG. 10, the excitation winding and torque winding ofthe stator are combined as a composite winding in which the sum ofexcitation and torque currents is to flow.

A non-illustrated speed control system for this motor is identical withthat of FIG. 3 except that the field-current control section is omittedand, instead, in the torque control section, the excitation currentcomponent of each stator winding also is obtained and is added to thetorque current component to create an individual current command IADS,IBES, ICFS.

The relation between the torque generation and the current in theindividual torque winding is shown in FIGS. 11(a) through 11(f) ascharacteristics relation between the individual current value and therotational angle RA.

The manner in which a counterclockwise torque corresponding to thecurrent amplitude IP1 is continuously generated will now be described.

When the-rotational angle RA gradually increases from zero, namely, therotor is rotating counterclockwise, the currents IAD, IBE, ICF of theindividual stator windings are controlled as shown in FIGS. 11(a), 11(b)and 11(c). A range of the rotor's rotational angle RA from 30 to 150degrees is shown on an enlarged scale in FIGS. 11(d), 11(e) and 11(f).

First, the induction voltages indicated by the broken lines in FIGS.11(d), 11(e) and 11(f) are identical with those of FIGS. 7(d), 7(e) and7(f) in terms of composite currents, except that the current IAD, IBE,ICF of each stator winding is the sum of each current of 7(d), 7(e) and7(f) and the excitation current component ID1. The obtained torquecharacteristics also identical with that of FIGS. 7(d), 7(e) and 7(f)except that the current load of each transistor of the power amplifiercircuit PW of FIG. 5 is increased when this motor is controlled by thespeed control system and that vibration and noise of the motor tend toincrease if the current controlling of the speed control system isdelayed from an ideal value by the load part of the excitation currentin high-speed rotation.

FIGS. 12(a) through 12(f) are time charts showing the manner in whichthe motor of FIG. 10 is controlled by a control method different fromthat of FIGS. 11(a) through 11(f).

In the control method of FIGS. 11(a) through 11(f), no torque isgenerated in the direction of torque command and even there is a currentcomponent to generate a reverse torque. Consequently, in the controlmethod of FIGS. 12(a) through 12(f), the current component of thisreverse torque is zeroed.

The manner in which a counterclockwise torque corresponding to thecurrent amplitude IP1 is continuously generated will next be described.

When the rotational angle RA gradually increases from zero, in otherwords, the rotor is rotating counterclockwise, the currents IAD, IBE,ICF of the individual stator windings are controlled as shown in FIGS.12(a), 12(b) and 12(c). A range of the rotor's rotational angle RA from30 to 150 degrees is shown on an enlarged scale in FIGS. 12(d), 12(e)and 12(f).

The current IAD is kept zero while the rotor's rotational angle iswithin a range of 0 to 65 degrees, is then increased from zero to IP2within a range of 65 to 75 degrees and is kept at IP2 within a range of75 to 110 degrees. Likewise in FIGS. 11(a) through 11(f), the inductionvoltage induced by the winding is indicated by dash-and-dot lines, andthe power, which is a product of the voltage and current, is suppliedfrom the speed control system to the motor. One part of this power willbe the magnetic energy inside the motor and the other part of the powerwill be a torque generated by the motor as a mechanical output. Within arange of 75 to 80 degrees, the voltage is gradually increased as theskewed end of the rotor salient pole enters the width of the confrontingstator salient pole, and the magnetic energy component of the power isaccumulated inside the motor whole the remaining power is converted intomechanical energy. Within a range of 80 to 105 degrees, the power(ID1×V1/2) is accumulated inside the motor as magnetic energy while theremaining power is converted as mechanical energy. The term "mechanicalenergy" refers chiefly to dynamic energy and a real load on the side ofthe load including the rotor. Within a range of 110 to 120 degrees, thecurrent IAD is decreased from IP2 to zero. In this range, the rotorsalient pole is located in perfect confronting relationship with theassociated stator salient pole so that no rotational attraction orrotational torque with respect to each other will be generated as anegative power, which is a product of voltage and current, is suppliedto the motor. Namely, magnetic energy inside the motor will be suppliedback to the power amplifier circuit PW. Thus mechanical energy issupplied to the motor as magnetic energy is supplied from the poweramplifier circuit PW to the motor and vice versa. In FIG. 12(d), unlikein FIG. 11(d), the current ID1 is kept zero while the rotor's rotationalangle RA is within a range of 0 to 65 degrees, and a clockwiserotational torque, which is a reverse rotational torque, is zero.Therefore, according to the control method of FIGS. 12(a) through 12(f),a rotational torque larger than that according to the control method ofFIGS. 11(a) through 11(f) because of no reverse rotational torque can beobtained. In this example, however, partly since it is necessary toconvert magnetic energy to the side of the power amplifier circuit PW ina short time, i.e., within a range of 110 to 120 degrees, and partlysince the voltage VS of the power amplifier circuit is limited, thehigh-speed-side rpm. which enables this control algorithm will belimited.

The current IBE is controlled in the same manner as the current IAD at atiming delayed in phase by 60 degrees from the current IAD, and thecurrent ICF is controlled in the same manner at a timing delayed inphase by 120 degrees from the current IAD. Subsequently, the samecontrolling is repeated for each phase in accordance with the rotor'srotational angle RA.

The control method of FIGS. 12(a) through 12(f) is advantageous in thatno reverse torque will be generated and, as a result, the rotationaltorque will be increased for the entire motor, but disadvantageous inthat the current load of each transistor of the power amplifier circuitPW will be increased as compared to the control method of FIGS. 7(a)through 7(f) and vibration and noise of the motor tend to increase ifthe current controlling of the speed control system is delayed from anideal value by the load components of the excitation current and voltagein high-speed rotation.

As an alternative method for supplying energy from the power amplifiercircuit to the motor in the high-speed-rotation range, the current IADmay be controlled in such a manner that a current larger than that ofFIG. 12(d) will flow as the terminal voltage of the motor is low whilethe rotor's rotational RA within a range of 60 to 80 degrees and will bedecreased before the rotational angle reaches 105 degrees. The samecontrol may be made for the currents IBE, ICF of the remaining phases.At that time, however, the torque ripple will be increased, so vibrationand noise will be increased. Because the frequencies of vibration andnoise are high in the high-speed-rotation range, practical designing ispossible, but depending on the uses.

FIG. 13 shows a further switched reluctance motor according to a fourthembodiment of the present invention.

The motor of this embodiment is differentiated from that of FIG. 1 inthat the relationship between the width of the individual rotor salientpoles and that of the individual stator salient poles is reversed.Specifically, in the rotor, each salient pole of 30 degrees in width isskewed by 5 degrees and hence has a maximum width, i.e., end-to-endwidth of 40 degrees. The width of the stator salient poles is 50degrees.

In the motor of this embodiment, as in that of FIG. 1, it is possible torealize a small torque ripple by varying the current of the torquewinding of each stator salient pole while the associated rotor salientpole is located perfectly in or out of confronting relationship with thestator salient pole through its circumferential surface. Further,likewise in the motor of FIG. 1, the torque winding may serve also asthe excitation winding.

This motor is advantageous, as compared to motor of FIG. 1, in that therotor inertia can be minimized and disadvantageous, as compared to themotor of FIG. 1, in that the stator windings are difficult tomanufacture due to the shape of the stator salient poles withoutincreasing the inter-turn space of the stator windings.

FIG. 14 shows the manner in which each of power amplifier circuits of afield-current control section are connected with a respective one ofstator windings in a still further switched reluctance motor accordingto a fifth embodiment of the present invention.

In the motor of this embodiment, pairs of windings WA, WAG; WB, WBG; WC,WCG; WD, WDG; WE, WEG; WF, WFG are mounted round each stator salientpole. The windings of each pair are magnetically coupled.

FIGS. 15(a) through 15(g) are time charts showing a very part of PWMcontrol operation of the power amplifier section of FIGS. 5 and 14. Tstands for a cycle of the control operation. Assuming that the PWMoperation is carried out at 10 kHz, the cycle in which each transistortakes an ON-OFF switching action is a very short time of 100 g sec.FIGS. 15(a), 15(b) and 15(c) show one example of the PWM operation ofthe power amplifier section of FIG. 5; specifically, FIG. 15(a) showscommand signals TAD of transistors 8, 9, FIG. 15(b), a voltage VPW to beapplied to the windings, and FIG. 15(c), a current IAD controlled in PWMoperation. FIGS. 15(d), 15(e), 15(f) and 15(g) show one example of PWMoperation of the power amplifier section of FIG. 14; specifically, FIG.15(a) shows command signals TAD of a transistor 12, FIG. 15(e), avoltage to be applied to the windings, FIG. 15(f), a current IADcontrolled in PWM operation, and FIG. 15(g), a current LAG controlled inPWM operation. If the currents IAD, IAG of FIGS. 15(f) and 15(g) arecombined, the resulting composite current is equal in value to thecurrent IAD of FIG. 15(c). More specifically, the transistor 12 isrendered to assume the ON state when the current IAD flows in the statorsalient poles, and if the transistor 12 is rendered to assume the OFFstate when the current IAD is increased, then the current IAD will bezero as the current path will disappear. At the same time, a voltagewill be generated also in the windings WAG, WDG and therefore thecurrent IAG will flow via a diode 13. This current is graduallydecreased as part of it flows back to the direct-current power sourcesVS, VL. By repeating this PWM control operation, the currents IAD, IAGare controlled with precision. Subsequently the same control operationis carried out for the remaining phases.

The power amplifier section of FIG. 14 is advantageous, as compared tothat of FIG. 5, in that the number of transistors and diodes can bereduced to half to reduce the cost of the control circuit anddisadvantageous in that the stator windings are complex to increasetheir resistance, thus lowering the motor efficiency.

FIG. 16 shows the manner in which the motor windings of FIG. 5 can bedivided and connected to selected intermediate portions of the statorwindings using switches according to a sixth embodiment of the presentinvention. In part because the current will flow in every winding duringthe low-speed rotation and partly since the voltage at the terminalvoltage of the motor will be increased during the high-speed rotation,the divided motor winding is connected to the intermediate portions ofthe stator winding to lower the terminal voltage of the motor so thatthe current can be supplied simply, thus realizing a high-speedrotational operation. Specifically, as shown in FIG. 16, in internalwindings and circuits between terminals PAD1, PAD2 of the motor, thestator windings WAT, WDT of FIG. 5 are respectively divided into twosets, WA1, WA2 and WD1, WD2 and selection can be made between thehigh-speed-rotation terminal SWH and the low-speed-rotation terminal SWLby the switch. The same operation is carried out for the remaining twophases.

A measure for minimizing the toque ripple in the switched reluctancemotor of FIG. 1 will now be described. In the foregoing description, thecharacteristics of the motor of FIG. 1 is modeled. Actually, however,partly since magnetic fluxes corresponding to the respective magneticresistances exist in the gaps between the circumferential surfaces andaxial surfaces of the rotor salient poles and stator salient poles, andpartly since the magnetic characteristics of silicon steel disks of themotor are non-linear magnetic saturation characteristics, there remaintorque ripple components that were unable to be eliminated only by theabove-mentioned simple theory. The remaining torque ripple componentsare divided by their respective high-frequency components, and the rotorstructure is improved in such a manner that these subdivided torqueripple components cancel one another to reduce the torque ripples. Withthe assumption that there exist torque ripple components in the cyclesTRP1, TRP2, the method in which these torque ripple components arereduced will now be described. The rotor, in the form of a laminate ofaxially arranged silicon steel disks, is axially divided into quartersRT1, RT2, RT3, RT4. The two quarters RT1 and RT2 are shifted in thedirection of rotation by a pitch of TRP1/2, and the two quarters RT3 andRT4 also are shifted in the direction of rotation by a pitch of TRP1/2.The first pair of quarters RT1, RT2 and the second pair of quarters RT3,RT4 are mutually shifted in the direction of rotation by a pitch ofTRP2/2. Thus it is theoretically possible to reduce the torque ripplesby independently canceling the individual high-frequency components ofthe torque ripples. Further, non-magnet bodies, such as of stainlesssteel, may be inserted into each axial interface of the rotor quartersRT1, RT2, RT3 and RT4 so that mutual magnetic couplings can be reducedto minimize the torque ripples more efficiently. Alternatively, insteadof dividing the rotor into quarters axially and shifting the rotorquarters in the direction of rotation, the stator may be axially dividedinto subdivisions and these subdivisions may be shifted in the directionof rotation.

In the first embodiment shown in FIG. 1, the torque ripples are reducedby skewing the rotor. As an effective alternative method, corners ofeach rotor salient pole, which are spaced apart in the direction ofrotation, may be shaped in a polygon or curved to assume a fan shape. Alow-torque-ripple characteristic can be realized by combining thisalternative with the above-mentioned torque-ripple minimizing measure.

FIG. 17 shows an additional switched reluctance motor according to aseventh embodiment of the present invention.

In FIG. 17, 1H designates a stator equipped with six stator magneticpoles each having a width substantially equal to and smaller than 60degrees in angle of rotation of the rotor. Each of excitation windingsindicated by HA3, HA4; HB3, HB4; HC3, HC4; HD3, HD4; HE3, HE4; HF3, HF4and each of torque windings indicated by HA1, HA2; HB1, HB2; HC1, HC2;HD1, HD2; HE1, HE2; HF1, HF2 are mounted round each stator magneticpole.

The label 3 designates a rotor equipped with a pair of opposite salientpoles having a width substantially equal to and smaller than 80 degreesin angle of rotation of the rotor. As long as the width PA of the rotorsalient poles is within a range of 60 to 120 degrees, it is possible toa positive/negative torque at every rotational position. As will also bedescribed below, the limit value of the width of the stator magneticpoles or rotor salient poles can be varied by skewing the rotor orstator.

As the speed control system for the motor, the circuit of FIG. 3 isused.

The relation between the generation of torque and the current of eachwinding is shown in FIGS. 18(a) through 18(e) and FIGS. 19(a) through19(e) in terms of characteristics of the individual current value andthe rotational angle RA.

The manner in which a counterclockwise torque corresponding to thecurrent amplitude IP1 is continuously generated will now be described.Firstly the value of the excitation current ID is constant ID1irrespective of the rotational angle RA as shown in FIG. 18(d).

Assuming that the rotational angle RA is gradually increased from zero,namely, the rotor is rotating counterclockwise, the current IAD in thewindings WAT, WDT is IP1 and the remaining currents IBE, ICF are zerowhen RA is zero. When the rotational angle RA is within 0 to 30 degrees,the windings WAT, WDT will generate a torque.

The current IBE in the windings WBT, WET is started increasing when RAreaches 20 degrees and is increased up to IP1 when RA reaches 30degrees. During that time, since the rotor salient pole has not yetreached the associated stator magnetic pole of the windings WBT, WET, notorque will be generated, which is a preparatory operation forsubsequent torque generation.

When the rotational angle RA is within a range of 30 to 90 degrees, thewindings WBT, WET will generate a torque. Simultaneously, within a rangeof 30 to 40 degrees, the current IAD will be described from IP1 to zero.During that time, since the stator magnetic pole round which thewindings WAT, WDT are mounted is located in confronting relation withthe associated rotor salient pole through its entire surface, nothingwill basically be contributed to generation of a torque.

Within a range of 80 to 90 degrees, the current ICF flowing in thewindings WC, WF is increased from zero to IP1 to make it ready togenerate a torque, and within a range of 90 to 150 degrees a torque isgenerated due to the current ICF. Simultaneously, within a range of 90to 100 degrees, the current IBE is increased from IP1 to zero.

Subsequently, as the individual current flows in the correspondingwindings, a counterclockwise constant torque with less torque ripplescan be continuously generated.

In each of characteristic charts of FIGS. 18(a) through 18(e), brokenlines indicate the induction voltage commensurate with variation of themagnetic flux crossing each winding of the motor. Accordingly, theamplitude of the induction voltage is proportional to the rotationalspeed. A voltage drop due to the variation of any possible leak magneticflux of the windings and the winding resistance may be neglected. Of theinduction voltages indicated by broken lines in FIGS. 18(a) through18(e), the induction voltage while the current in each phase flows maybe treated as the voltage feedforward signal IADS, IBES, ICFS. Also asignal corresponding to the induction voltage in the range where nocurrent flows may be added to the voltage feedforward signal; althoughthe necessity of a voltage feedforward signal corresponding to anegative voltage depends on the circuit type, such a voltage feedforwardsignal is usually not necessary. In order for more accurate control, thevoltage component corresponding to the variation of leak magnetic fluxof each winding and the dropped voltage component of the windingresistance also may be added to these induction voltage signals tocreate a voltage feedforward signal.

Since the width of the stator magnetic poles is 60 degrees and the widthof the rotor salient poles is 80 degrees, it is possible to expand theperiod of flow of current by quickening the front rise of current by,for example, approximately 5 degrees and delaying the back rise ofcurrent by, for example, approximately 5 degrees, so that the torque tobe generated by the motor will be constant. In view of increasingnecessity of varying the current at high speed during the high-speedrotation, expansion of the period of flow of current is effective insecuring a time margin in current control. By widening the width of thestator magnetic poles by, for example, approximately 90 degrees, it ispossible to increase the time margin in current control. However,limitless expansion of the period of current flow would increase copperloss from the motor so that efficient operation of the motor can not beachieved.

Consequently, for reducing the loss of the motor and thereby increasingthe output of the motor instead, it is preferable to minimize the periodof flow of current with the current control's time margin being set asthe limit. Specifically, as shown in the characteristic charts of FIGS.18(a) through 18(e), one effective method is to reduce the period offlow of current during the low-speed rotation and to expand the periodof flow of current with the increase of rpm. to such an extent that atime margin in current control can be obtained.

If the current, like the current IBE in the windings WBT, WET while RAis within a range of 20 to 30 degrees, flows in the windings while notorque is generated, magnetic energy will be accumulated and, soon afterthat, part of the accumulated magnetic energy will be converted intorotational energy, thus increasing the driving efficiency of a drivesystem.

The manner in which a clockwise torque corresponding to the current IP1is continuously generated will now be described. Firstly the excitationcurrent ID is constant as ID1, irrespective of the rotational angle RA,as shown in FIG. 19(d).

Assuming that the rotation angle RA is gradually increased, the currentICF is IP1 of the windings WCT, WFT when RA is zero, and the remainingtwo currents IAD, IBE are zero. While RA is within a range of 0 to 50degrees, the windings WCT, WFT generates a torque.

The current IAD in the windings WAT, WDT begins increasing when RAreaches 40 degrees and is increased to IP1 when RA reaches 50 degrees.During that time, since the stator magnetic pole round which thewindings WAT, WDT are mounted is located in confronting relation withthe associated rotor salient pole through its entire surface, nothingwill basically be contributed to generation of a torque. This is apreparatory operation for subsequent torque generation.

The windings WHT, WDT generates a torque while RA is within a range of50 to 110 degrees. During that time, when RA is 50 to 60 degrees, thewindings WCT and WFT do not generate a significant torque because thestator magnetic pole around which the winding WCT, WFT are mounted isnot located in a perfect confronting relationship with the associatesrotor salient pole.

The current IBE flowing in the windings WBT, WET is increased from zeroto IP1 while RA is within a range of 100 to 110 degrees, which makes itready to generate a torque, and a torque is generated due to the currentIBE while RA is within a range of 110 to 170 degrees. And the currentIAD is decreased from IP1 to zero while RA is within a range of 110 to120 degrees.

Subsequently, as the individual current flows in the correspondingwindings, a counterclockwise constant torque with fewer torque ripplescan be continuously generated.

In charts FIGS. 19(a) through 19(e), broken lines indicate the inductionvoltage commensurate with variation of the magnetic flux crossing eachwinding of the motor. Accordingly, partly since a power is the productof a positive current and a negative voltage, and partly since aclockwise torque is generated while the rotor is in counterclockwiserotation, the motor generates electric energy to perform regeneration.The amplitude of this induction voltage is proportional to therotational speed. A voltage drop due to the variation of any possibleleak magnetic flux of the windings and the winding resistance isneglected. Of the induction voltages indicated by broken lines in FIGS.19(a) through 19(e), the induction voltage while the current in eachphase flows may be treated as the voltage feedforward signal VAD, VBE,VCF.

The characteristics shown in FIGS. 19(a) through 19(e), as described inconnection with the operation when the counterclockwise torque isgenerated, are such that the period of flow of current can be expanded.The characteristics must depend on the width of the rotor salient poles.

The generation of torque is associated with the current in each phaseand the rotational position, but is not associated with the rotationaldirection and the rotational speed.

There exists a range of rotational angles RA such that the statormagnetic pole is located perfectly in or out of confronting relationshipwith the entire circumferential surfaces of the associated rotor salientpole, namely, no induction voltage of each windings is generated. Byvarying the current of the torque windings using this range ofrotational angle, it is for example possible to perform current controlwith less torque ripples.

The current control in which the subdivisions of the rotor as shown FIG.17 are individually skewed in the directional of rotation by 10 degreeswill now be described. Skewing of the rotor or stator minimizes torqueripples originating from the gap between adjacent stator magnetic poles.The voltage feedforward signal indicated by broken lines in FIGS. 18(a)through 18(e) and 19(a) through 19(e) has a rectangular waveform becausethe rotor salient poles are located perfectly in confrontingrelationship with the stator magnetic poles through their entirecircumferential surfaces when they reaches the stator magnetic poles sothat the magnetic flux varies stepwise. Skewing minimizes both vaguenessof signal in the interface regions where the voltage feedforward signalvaries with respect to the rotor's rotational angle RA in a rectangularwaveform and difficulty of instantaneously varying the voltage of thepower.

FIG. 18(e) is a chart showing the current IAD and the induction voltagein the windings when a counterclockwise torque is generated as the rotorskewed by 10 degrees is rotated in counterclockwise. Assuming that therotor is skewed by 10 degrees, the rate of variation of the magneticflux is increased linearly as the area of the confrontingcircumferential surfaces gradually increases when the skewedcircumferential part of the rotor reaches the stator magnetic poles, andthe rate of variation of the magnetic flux is kept constant after thestator magnetic poles have passed the skewed parts of the rotor. As aresult, the voltage signal varying stepwise can be changed into atrapezoidal waveform by gradually varying the voltage feedforwardsignal, thereby minimizing vagueness of signal in the interface regionand difficulty of sudden variation of the voltage. The higher the rateof rotation, the larger the result can be obtained.

If the current IAD is varied in the region where no induction voltage ofthe windings is generated, influence on the torque due to the currentvariation is small. Consequently varying the current around the regionwhere an effective voltage will be generated would suffice.

One phase in which the current IAD flows has been described. Theremaining two phases are delayed by 120 degrees and 240 degrees,respectively, with respect to the rotor's rotational angle RA, and thecontrol operation for these remaining phases is identical with that forthe first-named phase.

FIG. 19(e) is a characteristic chart showing the current IAD and theinduction voltage in the windings when a clockwise torque is generatedas the rotor skewed by 10 degrees is rotated in counterclockwise.Similarly, the voltage signal can also be changed into a trapezoidalwaveform, and the difficulty of current control can be minimized. Theremaining two phases are delayed by 120 degrees and 240 degrees,respectively, with respect to the rotor's rotational angle RA, and thecontrol operation for these remaining phases is identical with that forthe first-named phase.

FIG. 20 shows another switched reluctance motor according to an eighthembodiment of the present invention.

The motor of this embodiment differs from the motor of FIG. 17 in that acommon winding serves as both an excitation winding and a torque windingin the stator. In this embodiment, a value which is the sum of theexcitation current ID and each torque current, is controlled as a commonwinding current of each phase.

FIG. 21 shows a speed control system for this motor identical with thatshown in FIG. 3, except that no field-current control section isincluded.

The relationship between generation of torque and current of eachwinding is shown in a characteristic chart of FIG. 22 in terms of thecurrent value with respect to the rotational angle RA.

The manner in which a counterclockwise torque corresponding to thecurrent amplitude IP1 is continuously generated will now be described.Assuming that the rotational angle RA is gradually increased, in otherwords, the rotor is rotating counterclockwise, the current IAD of thewindings WAT, WDT is IP2 and the remaining currents IBE, ICF are ID1, asshown in FIG. 22(a). The value IP2 corresponds to the sum of theexcitation current ID1 and the torque current IP1 as shown FIG. 18.While the RA is within a range of 0 to 30 degrees, the windings WAT, WDTgenerates a torque.

The current IBE of the windings WBT, WET begins increasing when RAreaches 20 degrees, and the current value is increased to IP2 when RAreaches 30 degrees. Within this range, the rotor salient pole has notyet reached the associated stator magnetic pole of the windings WBT,WET, so no torque is generated.

When RA is within a range of 30 to 90 degrees, the windings WBT, WETgenerates a torque. Within a range of 30 to 40 degrees, the current IADis decreased from IP2 to ID1. At that point, since the stator magneticpole round which the windings WAT, WDT are mounted is located inconfronting relationship with the rotor salient pole through its entirecircumferential surfaces, basically no torque will be generated. Withina range of 80 to 90 degrees, the current ICF flowing in the windingsWCT, WFT is increased from ID1 to IP2 to make it ready to generate atorque, and within the range from 90 to 150 degrees the current ICFgenerates a torque. Within a range of 90 to 100 degrees, the current IBEis decreased from IP2 to ID1.

Likewise, with each current flowing, a counterclockwise constant torquewith less torque ripples can be continuously generated. The polarity ofthe rotor salient pole depends on the polarity of the associated statormagnetic pole. The distribution of the polarities of the rotor salientpoles is shown in FIG. 20 and is varied with rotation of the rotor.

In each of FIGS. 22(a) through 22(d), broken lines indicate inductionvoltages with variation of magnetic flux crossing each winding of themotor. Accordingly, the magnitude of the induction voltage isproportional to the rotational speed. And a voltage drip due to thevariation of leak magnetic flux of the winding and the windingresistance is neglected. The induction'voltages indicated by brokenlines in FIG. 22 are also voltage feedforward signals VAD, VBE, VCF ofthe individual phases. To achieve more accurate control, the voltagecomponent corresponding to the variation of leak magnetic flux of eachwinding and the dropped voltage component of the winding resistance alsomay be added to these induction voltage signals to create a voltagefeedforward signal.

Alternative control methods will now be described.

In FIGS. 22(a), 22(b) and 22(c), the excitation current ID1 may be zeroas indicated by dot lines. In such event, since excitation current iszero, the induction voltage indicated by broken (two dot) lines willnecessarily be zero. In this alternative, a larger torque can begenerated than the current value indicated by solid lines in FIGS.22(a), 22(b) and 22(c). The torque to be obtained by the excitationmagnetic current ID1 is the energy component of a characteristic ofelectromotive force H and magnetic flux density B, being half the torqueto be obtained by the torque current with respect to the same currentvalue.

At that time, the voltage feedforward signal IADS, IBES, ICFS is thesignal indicated by broken lines in FIGS. 22(a), 22(b) and 22(c). Thevoltage feedforward signal corresponding to the induction voltagecomponent indicated by dash-and-two-dot lines is not necessary.

The motor of FIG. 20 and the control characteristics of FIGS. 22(a),22(b) and 22(c) will now be described from an energy point of view, withpreconditions that the narrowest of the magnetic-flux-pass portionbetween the stator magnetic poles and the rotor salient poles is excitedat substantially saturation magnetic flux density by excitation currentID1, and that the magnetic characteristic of electromotive force H andmagnetic flux density B of the silicon steel disks constituting each ofthe stator magnetic poles and rotor salient poles is such that themagnetic flux density B increases linearly with the increase of theelectromotive force H and is substantially constant if it is oversaturation magnetic flux density.

If the current values of the individual phases are as indicated by solidlines in FIGS. 22(a), 22(b) and 22(c), the power P1 to be supplied fromthe control system of FIG. 21 to the motor is as expressed by Equation 1as the phase of the current IAD acts at an angular point, e.g., therotor's rotational angle RA=180 degrees.

    P1=(IP2)×(induction voltage VA)=(IP1+ID1)×(induction voltage VA)[Equation 1]

Of P1, (IP1)×(induction voltage VA) and 1/2 of (ID1)×(induction voltageVA) is the mechanical energy to be outputted as a torque. The remaining1/2 of (ID1)×(induction voltage VA) is the magnetic energy inside themotor which is to be supplied from the drive system of FIG. 21 into themotor.

In the meantime, the power P2 to be supplied from the motor back to thedrive system of FIG. 21 is as expressed by Equation 2 as the phase ofthe current ICF acts.

    P2=-(ID1)×(induction voltage VA)                     [Equation 2]

1/2 of P2 is the mechanical energy to be supplied back to the drivesystem of FIG. 21 as a rotational torque and a reverse torque, and theremaining 1/2 of P2 is supplied from inside the motor back to the drivesystem of FIG. 21.

As a result, the mechanical output power P3 of the motor can beexpressed by Equation 3.

    P3=P1-P2=(IP1)×(induction voltage VA)                [Equation 3]

In FIGS. 22(a), 22(b) and 22(c), in the range where the current value ofeach phase is an excitation current ID1, the current value may be zeroas indicated by dotted lines. The motor of FIG. 20 and the controlcharacteristics of FIGS. 22(a), 22(b) and 22(c) will now be describedfrom an energy point of view. If the current values of the individualphases are as indicated by solid lines in FIGS. 22(a), 22(b) and 22(c),the power P1 to be supplied from the control system of FIG. 21 to themotor is as expressed by Equation 4 as the phase of the current IAD actsat an angular point, e.g., the rotor's rotational angle RA=180 degrees.

    P1=(IP2)×(induction voltage VA)=(IP1+ID1)×(induction voltage VA)[Equation 4]

Of P1,(IP1)×(induction voltage VA) and 1/2 of (ID1)×(induction voltageVA) is the mechanical energy to be outputted as a torque. The remaining1/2 of (ID1)×(induction voltage VA) is the magnetic energy inside themotor which is to be supplied from the drive system of FIG. 21 into themotor.

In the meantime, the power P2 to be supplied from the motor back to thedrive system of FIG. 21 is nil partly since the current ICF is zero andpartly since-no excitation current flows, namely, the induction voltageis zero, causing no energy to be input or output.

As a result, the mechanical output power P3 of the motor can beexpressed by Equation 5.

    P3=P1-(ID1)×(induction voltage VA)×1/2-P2=P1-(ID1)×(induction voltage VA)×1/2=(IP1+ID1/2)×(induction voltage VA)    [Equation 5]

Of P1, 1/2 of (ID1)×(induction voltage VA) is the magnetic energy insidethe motor which does not contribute to output torque.

The motor of FIG. 20 is advantageous in that the windings are simplifiedas compared to the motor of FIG. 17 and that the control circuit doesnot require the excitation circuit of FIG. 4 and is hence simplified anddisadvantageous in that the voltage of the motor terminals during thehigh-speed rotation is higher as compared to the motor of FIG. 17 toincrease the load of the current control section and that only theexcitation current component of the motor current is increased tonecessitate increasing the current capacitance of the current controlsection. Accordingly, since the motor of FIG. 17 and the motor of FIG.20 have merits and demerits depending on the rpm. and output power, themotor of FIG. 3 is usually advantagous during high-speed rotation orwhen the output power is large.

Current control with the rotor of FIG. 20 skewed in the direction ofrotation by 10 degrees will next be described. When the rotor is tiltedby 10 degrees, the rate of variation of the magnetic flux is increasedlinearly as the area of the confronting circumferential surfacesgradually increases when the skewed circumferential part of the rotorreaches the stator magnetic poles, and the rate of variation of themagnetic flux is kept constant after the stator magnetic poles havepassed the skewed parts of the rotor. As a result, the voltage signalvarying stepwise can be changed into a trapezoidal waveform by graduallyvarying the voltage feedforward signal, thereby minimizing vagueness ofsignal in the interface region and difficulty of sudden variation of thevoltage.

FIG. 22(d) shows a specific control characteristic for the phase ofcurrent IAD. The induction voltage is a characteristic indicated bybroken lines in FIG. 22(d). As described above, the current IADindicated by solid lines maybe changed to that indicated by dottedlines, in which event the induction voltage indicated by broken (twodot) lines is zero.

The remaining two phases of current IBE, ICF are delayed by 120 degreesand 240 degrees, respectively, with respect to the rotor's rotationalangle RA, and the control operation for these remaining phases isidentical with that for the first-named phase.

Various modifications and changes to the foregoing switched reluctancemotors and control systems are possible.

For example, each arithmetic section illustrated as an example of thecontrol system of FIG. 3 may be substituted by a micro processor and amemory for storing a control pattern so that the same control can berealized. Other alternatives are fuzzy control and neural-net-memorycontrol.

The method of detecting the rotational position of the rotor may besensorless and not empty.

In controlling the high-speed rotation of the motor, the excitationcurrent may be weakened, namely, the intensity of field may be weakened,enabling a wide selection of applications.

The number of the stator magnetic poles and that of the rotor salientpoles may be decreased to 3 and 2, respectively, or increased.

Although in certain described embodiments, the rotor is skewed,alternatively, the stator may be skewed. The rotor may be axiallydivided into several parts shifted at a small pitch in the direction ofrotation with the same result as skewing.

Further, the control mode may be automatically switched to meet the moresuitable of the rotational conditions of the motor. This alternativemethod is exemplified by a method of switching the control algorithmbetween the low-speed rotation and the high-speed rotation and a methodof gradually transferring from the low-speed rotation to the high-speedrotation and vice versa.

According to the switched reluctance motor and control system of thepresent invention, it is possible to minimize torque ripples, thusrealizing a drive system with less vibration and noise. To control thethree-phase induction motor, common power amplifier sections usuallyrequire six transistors and six diodes. However, in the presentinvention, only three transistors and three diodes are required so thatan inexpensive control system can be realized and ahigher-speed-rotation drive can be achieved. Further, because of thetorque-ripple-minimizing measure, it is possible to more silently drivemotors at high speeds.

What is claimed is:
 1. A motor control system for controlling a motor,which includes six stator magnetic poles each having a widthsubstantially equal to or less than 60 degrees in terms of angle ofrotation of a rotor, excitation windings mounted one round each of thestator magnetic poles, torque windings mounted one round each statormagnetic pole, and two rotor salient poles each having a width rangingfrom 60 degrees to 120 degrees in terms of angle of rotation of therotor, said system comprising:(a) an excitation drive circuit adapted toconnect said excitation windings in series for supplying adirect-current-exciting current to each excitation winding to excite themotor in accordance with an excitation command signal; and (b) atorque-current drive circuit for causing, when a torque command ispositive, a current having a magnitude in accordance with the torquecommand to flow in the torque winding of the stator magnetic pole atwhich a counterclockwise end of the associated rotor salient poles andfor causing, when the torque command is negative, said current to flowin the torque windings of the stator magnetic pole at which a clockwiseend of the associated rotor salient poles.
 2. A motor control systemaccording to claim 1,wherein when the torque command is positive whilethe rotor is rotating counterclockwise, a torque current in the torquewinding on each stator magnetic pole is controlled in such a manner thatsaid torque current is increased while the counterclockwise end of eachrotor salient pole is located counterclockwise of the clockwise end ofthe associated stator magnetic pole and that said torque current in thetorque winding on each stator magnetic pole is decreased while theclockwise end of the rotor salient pole is located counterclockwise ofthe counterclockwise end of the associated stator magnetic pole, andwherein, when the torque command is negative while the rotor is rotatingcounterclockwise, said torque current is controlled in the torquewinding on each stator magnetic pole in such a manner that said torquecurrent is increased while each stator magnetic pole is located within awidth of the associated rotor salient pole and that said torque currentis decreased while none of the stator magnetic poles are located inconfronting relationship with any of the rotor salient poles throughouttheir circumferential surfaces.
 3. A motor control system forcontrolling a motor, which includes a rotor having two salient poleseach having a width ranging from 60 to 120 degrees in terms of angle ofrotation of the rotor, a stator surrounding the rotor, the stator havingsix stator magnetic poles each having a width substantially equal to orsmaller than 60 degrees in terms of angle of rotation of the rotor,common windings mounted one round each of the stator magnetic poles, anda common-winding-current drive circuit,wherein said system has acommon-winding-current drive circuit for obtaining an excitation currentsuch as to excite the motor in accordance with an excitation commandsignal, for obtaining a torque current such as to have a magnitude inaccordance with a torque command and to flow in the command winding ofeach stator salient pole, at which a counterclockwise end of theassociated salient pole is located when the torque command is positiveor a clockwise end of the associated salient pole is located when thetorque command is negative, and for rendering a composite current, whichis a sum of said excitation current and said torque current, to flow ineach common winding.
 4. A motor control system according to claim 3,wherein:when the torque command is positive while the rotor is rotatingcounterclockwise, said torque current is controlled in the torquewinding on each stator magnetic pole in such a manner that said torquecurrent is increased while the counterclockwise end of each rotorsalient pole is located counterclockwise of the clockwise end of theassociated stator magnetic pole and that said torque current in thecommon winding on each stator magnetic pole is decreased while theclockwise end of the rotor salient pole is located counterclockwise ofthe counterclockwise end of the associated stator magnetic pole, andwhen the torque command is negative while the rotor is rotatingcounterclockwise, said torque current is controlled in the commonwinding on each stator magnetic pole in such a manner that said torquecurrent is increased while each stator magnetic pole is located within awidth of the associated rotor salient pole and that said torque currentis decreased while none of the stator magnetic poles are located inconfronting relationship with any of the rotor salient poles throughouttheir circumferential surfaces.
 5. A motor control system according toclaim 2, wherein:when the torque command is positive while the rotor isrotating counterclockwise, said torque current is controlled in thecommon winding on each stator magnetic pole in such a manner that saidtorque current is increased while the counterclockwise end of each rotorsalient pole is located counterclockwise of the clockwise end of theassociated stator magnetic pole by a RA angle and that said torquecurrent in the common winding on each stator magnetic pole is decreasedwhile the clockwise end of the rotor salient pole is locatedcounterclockwise of the counterclockwise end of the associated statormagnetic pole by said RA angle, when the torque command is negativewhile the rotor is rotating counterclockwise, said torque current iscontrolled in the common winding on each stator magnetic pole in such amanner that said torque current is increased while the clockwise end ofeach rotor salient pole is located clockwise of the clockwise end of theassociated magnetic pole by said RA angle and that said torque currentis decreased while the clockwise end of each rotor salient pole islocated clockwise of the counterclockwise end of the associated statormagnetic pole by said RA angle, and wherein said RA angle is small whenthe rate of the rotation of the motor is small and is large when therate of the rotation of the motor is large.
 6. A motor control systemaccording to claim 4, wherein:when the torque command is positive whilethe rotor is rotating counterclockwise, said torque current iscontrolled in the common winding on each stator magnetic pole in such amanner that said torque current is increased while the counterclockwiseend of each rotor salient pole is located counterclockwise of theclockwise end of the associated stator magnetic pole by a RA angle andthat said torque current in the common winding on each stator magneticpole is decreased while the clockwise end of the rotor salient pole islocated counterclockwise of the counterclockwise end of the associatedstator magnetic pole by said RA angle, when the torque command isnegative while the rotator is rotating counterclockwise, said torquecurrent is controlled in the common winding on each stator magnetic polein such a manner that said torque current is increased while theclockwise end of each rotor salient pole is located clockwise of theclockwise end of the associated magnetic pole by said RA angle and thatsaid torque current is decreased while the clockwise end of each rotorsalient pole is located clockwise of the counterclockwise end of theassociated stator magnetic pole by said RA angle, and wherein said RAangle is small when the rate of the rotation of the motor is small andis large when the rate of the rotation of the motor is large.
 7. A motorcontrol system according to claim 1, including a plurality ofregenerative windings mounted one on each stator magnetic pole, andfurther comprising a plurality of diodes each connected in seriesbetween each of the regenerative windings and a power source of themotor for utilizing part of the magnetic energy of each stator magneticpole to rotate the motor and supplying the other part of the magneticenergy back to the power source, each of said diodes having an anodeconnected to a low-voltage side of the power source and a cathodeconnected to a high-voltage side of the power source.
 8. A motor controlsystem according to claim 3, including a plurality of regenerativewindings mounted one on each stator magnetic pole, and furthercomprising a plurality of diodes each connected in series between eachof the regenerative windings and a power source of the motor forutilizing part of the magnetic energy of each stator magnetic pole torotate the motor and supplying the other part of the magnetic energyback to the power source, each of said diodes having an anode connectedto a low-voltage side of the power source and a cathode connected to ahigh-voltage side of the power source.